1. Field of the Invention
The present invention relates to a circuit device in which a semiconductor element is thinly covered with a sealing resin mixed with filler particles and to a method of manufacturing the circuit device.
2. Description of the Related Art
A manufacturing process of a circuit device mainly includes: a front-end process in which desired elements are incorporated into a surface of a single semiconductor wafer; and a back-end process in which packaging is performed on the semiconductor elements obtained by dividing the semiconductor wafer into pieces.
In recent years, there has been developed a manufacturing method in which multiple circuit devices are sealed by a resin in a single sealing step, the resultant resin-sealed body is divided by dicing to obtain separate circuit devices. This technology is described for instance in Japanese Patent Application Publication No. 2000-164609.
With reference to FIGS. 8A to 8D, the above-mentioned method of manufacturing a circuit device will be described. FIGS. 8A to 8D are cross sectional views each showing a manufacturing step.
Referring to FIG. 8A, firstly, conductive patterns 102 and semiconductor elements 106, which constitute a large number of circuit devices, are arranged on an upper surface of a substrate 100. The substrate 100 is made of ceramic or a resin material and the multiple conductive patterns 102 are formed on the upper surface of the substrate 100. Here, a unit 108 to serve as one circuit device is constituted of multiple conductive patterns 102. Each of the semiconductor elements 106 is fixed on a corresponding one of the conductive patterns 102 of the unit 108, and an electrode of the semiconductor element 106 is connected to a different one of the conductive patterns 102 via a thin metal wire 104.
Referring to FIG. 8B, a sealing resin 110 is applied to the upper surface of the substrate 100 so as to cover the multiple units 108. The sealing resin 110 is made of a resin mixed with granular filler particles of silica (SiO2) or the like. The sealing resin 110 in a liquid or semisolid state is provided on the upper surface of the substrate 100 and then hardened.
Referring to FIG. 8C, grinding is then performed on the top surface of the sealing resin 110, so that the sealing resin 110 is made thinner and the top surface of the sealing resin 110 is planarized.
Referring to FIG. 8D, subsequently, the sealing resin 110 and the substrate 100 are divided by dicing at boundaries of the units 108 to obtain separate circuit devices.
With the above manufacturing steps, a large number of circuit devices are collectively manufactured. This leads to an advantage that productivity of the circuit devices is improved.
However, when the sealing resin 110 shown in FIG. 8C is made thin so that the circuit devices to be manufactured can be thin, the aforementioned manufacturing method poses a problem that the thin metal wires 104 show through the covering sealing resin 110.
Specifically, the sealing resin 110 used for resin sealing is made of a resin material containing filler particles of silica or the like. Silica is a transparent material which transmits light easily. This means that, when the top surface of the sealing resin 110 is ground so that the sealing resin 110 covering the thin metal wires 104 would be thinner, i.e., approximately 50 μm thin, light from the outside easily reaches the thin metal wires 104 through the filler particles.
FIG. 9 is an image obtained by shooting a cross section of a conventional circuit device, showing a taken image of the thin metal wire 104 and the sealing resin 110 covering the thin metal wire 104. In this image, the top surface of the sealing resin 110 is shown by a dotted line and a filler particle partially exposed to the outside from the top surface of the sealing resin 110 is encircled by a white oval.
Referring to this image, the thickness of a portion, covering the thin metal wire 104, of the sealing resin 110 is approximately 50 μm, for example, and might be smaller than the diameter of the filler particle. This produces a portion in which the thin metal wire 104 is covered with the filler particle only, not with the resin material. Since the filler particle is more transparent than the resin material, light from the outside easily reaches the thin metal wire 104 through the filler particle. Consequently, the thin metal wire 104 shows through the filler particle. This show-through of the thin metal wire 104 detracts from the external appearance of the circuit device.